Method of assembling a hybrid inflator

ABSTRACT

A hybrid inflator for an automotive inflatable safety system and method for assembling the same. In one embodiment, a mixture of an inert gas (e.g., argon) and oxygen are contained within the inflator housing and a gun type propellant is used in the gas generator to supply the propellant gases.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.08/210,668 filed Mar. 18, 1994.

FIELD OF THE INVENTION

The present invention generally relates to the field of automotiveinflatable safety systems and, more particularly, to hybrid inflatorswhich utilize both a stored, pressurized gas and a gas generatingpropellant.

BACKGROUND OF THE INVENTION

The evolution of inflators for automotive inflatable safety systems hasresulted in the development of pressurized gas only inflators,propellant only inflators, and hybrid inflators. Hybrid inflatorsutilize a combination of a stored, pressurized gas and gas generatingpropellant to expand the air/safety bag. There are of course many designconsiderations for of each of these types of inflators. In all threesystems, two primary design considerations are that the air/safety bagmust be expanded a predetermined amount in a predetermined amount oftime in order to be operationally effective. Moreover, since the gaswithin the expanded air/safety bag eventually permeates through theair/safety bag and is discharged to atmosphere, the effect of the gasesupon occupants of the automobile is important.

With further regard to the effect of the gases upon the occupants, forinstance it is desirable to have the gases within the air/safety bag bebelow a certain toxicity level. U.S. Pat. Nos. 3,690,695; 3,788,667; and3,966,226 generally address this issue. Moreover, the appearance of thegases is important. As an example, one problem with currentstate-of-the-art hybrid inflators is that they produce, in the gasoutput stream, copious quantities of metal salt fumes (e.g., potassiumchloride). This salt is present because an oxygen source must be addedto the propellant formulation to minimize carbon monoxide production byoxidizing all carbon in the propellant to carbon dioxide. This salt fumeis highly objectional in a crash situation because it has bothphysiological and psychological effects, imposed in a time of greatphysical and psychological stress. The salt fume in the post-crashautomobile cabin drastically reduces visibility for the crash victims,and creates anxiety over the possibility of fire. Current hybridinflators use propellants which typically contain more than 70%potassium perchlorate, which yields about 54% of the propellant weightas potassium chloride fume.

Since the weight of the automobile is an important design considerationin many instances today, so to then is the weight of the inflator.Moreover, due to the limited space available in many automotive designs,the size of the inflator is also an important design consideration.These types of factors have effectively rendered pressurized gas onlyinflators obsolete. Moreover, in propellant only and hybrid inflators,these types of considerations have resulted in many changes to thestructure of the inflator and the materials selected for use in thisstructure. However, little consideration has been given to thepropellant to achieve a certain weight reduction.

Although the performance of a given inflator will of course influencethe manufacturer's/supplier's position in the marketplace, systemperformance alone is no longer dispositive. That is, since inflatablesafety systems are now being included in a large number of automobileswhich will likely increase the number of manufacturers/suppliers ofinflators, minimizing the cost of the inflator is becoming increasinglyimportant to obtaining a competitive advantage. Consequently, it wouldbe desirable to not only provide an inflator with competitiveperformance characteristics, but which is also cost competitive.

SUMMARY OF THE INVENTION

The present invention is generally directed to a hybrid inflator for anautomotive inflatable safety system. That is, the invention relates toan inflator which utilizes both a stored, pressurized gas and a gasgenerating propellant. More specifically, the various aspects of thepresent invention are embodied in a hybrid inflator which usespropellants which produce large amounts of carbon monoxide and hydrogen.This would normally be unacceptable in an inflator for an automotiveinflatable safety system. However, these combustion products areconverted to harmless carbon dioxide and water vapor by oxygen which isused as at least part of the stored, pressurized gas of the hybridinflator. This stored oxygen eliminates the need for an oxygen source(e.g., potassium perchlorate) in the propellant formulation, and therebyeliminates the largest source of objectionable particulate fumeproduction in the inflator. This reaction of carbon monoxide andhydrogen produced by the propellant with the oxygen stored in theinflator as a gas also greatly enhances the heating value of thepropellant, thereby minimizing the amount of propellant required.

One aspect of the present invention is directed toward a hybrid inflatorwhich utilizes a gun type propellant in the gas generator for generatingthe propellant gases. Gun type propellants, as used herein, are hightemperature, fuel-rich propellants such as single, double, ortriple-base propellants, and nitramine propellants such as LOVA orHELOVA propellants. More specifically, gun type propellants are thosehaving a combustion temperature ranging from about 2500 K. to about 3800K., and typically greater than about 3000 K., and are fuel-rich in thatwithout excess oxygen, these propellants generate significant amounts ofCO and H₂. The excess of fuel from these propellants typically requiresadditional oxygen between 15 and 40 mole percent to drive theequilibrium to CO₂ and H₂ O. One particular propellant which hasperformed desirably is an M39 LOVA propellant available from the NavalOrdnance Station in Indianhead, Md. and Bofors in Europe. Thisparticular propellant, without the excess oxygen, generates about 32mole percent CO and about 30 mole percent H₂. However, the M39 LOVApropellant does satisfy current U.S. automotive industry tests relatingto propellants (e.g., it does not degrade sufficiently to severelyimpact performance when exposed to a temperature of 107° C. for a periodof 400 hours). In contrast, many if not most existing double-basepropellants cannot meet this standard partly because they containnitrocellulose as a major ingredient. Therefore, M39 LOVA propellantsare preferred over existing double-base propellants with regard to thepresent invention, although a further improvement to completelyeliminate nitrocellulose from M39 LOVA would be desirable.

With regard to this initial aspect of the present invention, it may bedesirable to utilize multiple stored gases within the inflator housing.For instance, one of the gases may be an inert gas such as argon and maycomprise a majority of the stored gas, while the other gas may beoxygen. Argon has advantages such as that it is relatively inexpensive,inert, has a relatively large molecule and thus is relatively easy tostore at a high pressure (e.g., 3,000 psi) for an extended period oftime, and has a low heat capacity. Oxygen is advantageous in that itwill react with the propellant gases and provide multiple functions.Initially, this reaction generates heat which further contributes to theexpansion of the argon by the propellant gases which allows for usingreduced amounts of propellant. Moreover, the noted reaction may reducethe toxicity of the propellant gases by driving the reaction equilibriumto CO₂ and H₂ O. This use of multiple gases for the stored, pressurizedgas in the hybrid inflator may also provide benefits when used withother propellants.

Another aspect of the present invention is directed toward a method forassembling a hybrid inflator. The method generally includes the steps ofpositioning a gun type propellant in the gas generator, interconnectingthe gas generator and inflator housing, introducing a first gas into theinflator housing, introducing a second gas into the inflator housingwhich is different from the first gas, and sealing the inflator housingto retain the first and second gases therein. In this aspect, theamounts of gun type propellant and the size and weight of the inflatormay be as noted above. Moreover, in this aspect the first gas may beargon and the second gas may be oxygen, with the argon being about 70%to about 90% of the stored gas in the inflator housing on a molar basisand the oxygen being about 10% to about 30% on a molar basis.Stoichiometrically, a lesser amount of oxygen is actually required, butfor reasons of kinetics a significant excess over stoichiometric isrequired to react with the objectionable gases. This multiple gasconfiguration provides the above-noted advantages, and may also bebeneficial to use with other propellants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an automotive inflatable safetysystem;

FIG. 2 is a longitudinal cross-sectional view of a hybrid inflator whichmay incorporate one or more principles of the present invention;

FIG. 3 is an inflator internal pressure versus time performance curvefor the propellant composition of Example 2; and

FIG. 4 is a receiving tank pressure versus time performance curve forthe propellant composition of Example 2.

DETAILED DESCRIPTION

The present invention will be described with regard to the accompanyingdrawings which assist in illustrating various features of the invention.In this regard, the present invention generally relates to hybridinflators for automotive inflatable safety systems. That is, theinvention relates to an inflator which utilizes both a stored,pressurized gas and a gas generating propellant. Various types of hybridinflators are disclosed in U.S. Pat. No. 5,230,531 to Hamilton et al.which is assigned to the assignee of this application, and the entiredisclosure of this patent is hereby incorporated by reference in itsentirety herein.

One embodiment of an automotive inflatable safety system is generallyillustrated in FIG. 1. The primary components of the inflatable safetysystem 10 include a detector 14, an inflator 26, and an air/safety bag18. When the detector 14 senses a condition requiring expansion of theair/safety bag 18 (e.g, a predetermined deceleration), a signal is sentto the inflator 26 to release gases or other suitable fluids from theinflator 26 to the air/safety bag 18 via the conduit 22.

The inflator 30 illustrated in FIG. 2 is a hybrid inflator and may beused in the inflatable safety system 10 of FIG. 1 in place of theinflator 26. Consequently, the inflator 30 includes a bottle or inflatorhousing 34 having a pressurized medium 36 that is provided to theair/safety bag 18 (FIG. 1) at the appropriate time, as well as a gasgenerator 82 that provides propellant gases to augment the flow to theair/safety bag 18 (e.g., by providing heat to expand the pressurizedmedium 36). As will be discussed in more detail below, it has beendetermined that it is desirable to utilize a gun type propellant asdefined above in the gas generator 82 and to utilize a mixture of oneinert gas (e.g., argon) and oxygen for the pressurized medium 36.

The inflator housing 34 and gas generator 82 are interconnected, withthe gas generator 82 being positioned inside the inflator housing 34 toreduce the space required for the inflator 30. More specifically, ahollow diffuser 38 is welded to one end of a hollow boss 66. Thediffuser 38 has a plurality of rows of nozzles 40 therethrough whichprovides a "non-thrusting output" from the inflator 30 and a screen 58is positioned adjacent the nozzles 40. A closure disk 70 isappropriately positioned within the boss 66 and is welded thereto inorder to initially retain the pressurized medium 36 within the inflatorhousing 34. When release is desired, a projectile 50 having asubstantially conically-shaped head is propelled through the closuredisk 70. More particularly, the projectile 50 is positioned on theconvex side of the closure disk 70 within a barrel 54 and is propelledby the activation of an initiator 46 when an appropriate signal isreceived from the detector 14 of the inflatable safety system 10 (FIG.1). A ring 62 is provided to initially retain the projectile 50 inposition prior to firing.

An orifice sleeve 74 is welded to the closure disk 70 and/or the end ofthe boss 66. The orifice sleeve 74 is hollow and includes a plurality oforifice ports 78 to fluidly interconnect the interior of the inflatorhousing 34 and the interior of the boss 66 and diffuser 38 when theclosure disk 70 is ruptured by the projectile 50. Moreover, the gasgenerator 82, more specifically the gas generator housing 86, is weldedto the orifice sleeve 74 to complete the interconnection of the inflatorhousing 34 and gas generator 82.

The gas generator housing 84 contains a plurality of propellant grains90 which when ignited provides propellant gases through the gasgenerator nozzle 98 for augmenting the flow to the air/safety bag 18(FIG. 1). The propellant grains 90 are retained within the gas generatorhousing 86 by a propellant sleeve 94 which is separated from the gasgenerator nozzle 98 on the discharge end 96 of the gas generator housing86 by a screen 104 and baffle 100. As will be discussed below, thepropellant grains 90 in one aspect are composed of a gun typepropellant. In this case, the grains 90 are substantiallycylindrically-shaped with a single hole extending through the centralportion thereof. Other propellant grain configurations may beappropriate and will depend at least in part on the composition of thepropellant.

The gas generator 82 includes an ignition assembly 114 for igniting thepropellant grains 90 at the appropriate time. The ignition assembly 114is at least partially positioned within the gas generator housing 86between the projectile 50 and propellant grains 90 and generallyincludes an actuation piston 124, and at least one percussion primer 120and an ignition/booster material 144 which serve as an activator. Moreparticularly, an actuation guide 140 engages an end portion of theorifice sleeve 74 and the interior wall of the gas generator housing 86,the actuation guide 140 thereby functioning at least in part to containat least a portion of and guide the actuation piston 124 positionedtherein. A primer holder 116 engages an end of the actuation guide 140and houses a plurality of conventional percussion primers 120 which arepositioned substantially adjacent to the ignition/booster material 144.The ignition/booster material 144 is typically retained adjacent theprimers 120 by a charge cup 148. A retainer 108 and baffle 112 arepositioned between the primer holder 116 and propellant sleeve 94. Inthe event that the gas generator housing 86 is attached to the orificesleeve 74 by crimping versus welding, the gas generator housing 86 mayhave a tendency to lengthen during operation. Consequently, in order tomaintain a firm interaction of the foregoing components, a wave springwasher (not shown) may be positioned, for instance, between the retainer108 and the baffle 112.

The actuation piston 124 is slidably positioned within the actuationguide 140 and includes a continuous rim projecting member 128 which issubstantially aligned with the primers 120. As can be appreciated, aplurality of projecting members (not shown), could replace thesubstantially continuous rim projecting member 128. A belleville washer136 is positioned between and engages a portion of both the actuationguide 140 and actuation piston 124 (via a spacer 126) to initiallymaintain the position of the actuation piston 124 away from the primers120. Consequently, the potential for inadvertent engagement of theactuation piston 124 with the primers 120, which could activate the gasgenerator 82, is reduced. However, after the projectile 50 passesthrough the closure disk 70, the energy transferred to the actuationpiston 124 by the projectile 50 is sufficient to overcome the bellevillewasher 136 such that the projecting rim 128 is able to engage theprimers 120 with sufficient force to ignite at least one of such primers120. This in turn causes ignition of the ignition/booster material 144,and thus ignition of the propellant grains 90.

During operation of the gas generator 82, the primers 120 may erode andthereby allow propellant gases generated by combustion of the propellantgrains 90 to flow through the primers 120. Any leakage of propellantgases in this manner may adversely affect the consistency of performanceof the inflator 30. These gases, however, desirably act upon theactuation piston 124 to move the piston 124 into sealing engagement withthe actuation guide 140. This provides a seal for the gas generatorhousing 90 which substantially limits any leakage of gases therethrough.Therefore, the propellant gases desirably flow through the gas generatornozzle 98.

Summarizing the operation of the inflator 30, the detector 14 (FIG. 1)sends a signal to the initiator 46 to propel the projectile 50. Theprojectile 50 initially passes through the closure disk 70 to open thepassageway between the inflator housing 34 and air/safety bag 18 (FIG.1). The projectile 50 continues to advance until it impacts theactuation piston 124 which causes the projecting rim 128 attachedthereto to strike at least one of the aligned primers 120. As a result,the ignition/booster charge 144 ignites, which in turn ignites thepropellant grain 90. The resulting propellant gases exit the gasgenerator nozzle 98 positioned on the discharge end 96 of the gasgenerator housing 86 and flow into the inflator housing 34 to providethe desired function, that of augmenting the flow to the air/safety bag18 (FIG. 1).

As noted above, the hybrid inflator 30 utilizes a gun type propellantcomposition for the propellant grains 90 and a mixture of an inert gasand oxygen for the pressurized medium 36. Initially, gun typepropellants are defined above, that is propellants which have a highcombustion temperature and which are fuel-rich. Specific gun typepropellants which may be used for the propellant grains 90 of the hybridinflator 30 include HPC-96, a double base, smokeless propellant having acomposition, on a weight percentage basis, of about 76.6% nitrocelluloseof which about 13.25% is nitrogen; about 20.0% nitroglycerin; about 0.6%ethyl centralite; about 1.5% barium nitrate; about 0.9% potassiumnitrate; and about 0.4% graphite. HPC-96 is available from Hercules,Inc. in Wilmington, Del. LOVA propellants (low vulnerability ammunition)and HELOVA propellants (high energy, low vulnerability ammunition) mayalso be used for the propellant grains 90, such as a M39 LOVA propellanthaving a composition, on a weight percentage basis, of about 76.0% RDX(hexahydrotrinitrotriazine); about 12.0% cellulose acetate butyrate;about 4.0% nitrocellulose (12.6% nitrogen); about 7.60% acetyl triethylcitrate; and about 0.4% ethyl centralite. The M39 LOVA propellant isavailable from the Naval Ordnance Station in Indianhead, Md. and Boforsin Europe. The LOVA and HELOVA propellants are preferred over existingdouble-base propellants since they pass current U.S. automotive industrystandards, whereas double-base propellants do not.

Due to the performance characteristics of gun type propellants when usedfor the propellant grains 90, together with the use of oxygen as aportion of the pressurized medium 36, it is possible to reduce theamount of propellant required for the gas generator 82 compared tocurrent designs using, for example, FN 1061-10 available from theassignee of this patent application (FN 1061-10 has a composition, on aweight percentage basis, of about 7.93% polyvinyl chloride, 7.17%dioctyl adipate, 0.05% carbon black, 0.35% stabilizer, 8.5% sodiumoxalate, 75% potassium perchlorate, and about 1% lecithin). Forinstance, when the desired gun type propellant composition is used forthe propellant grains 90 the total grain weight may range from about 10grams to about 12 grams, and is preferably less than about 15 grams. Inthis case, it is preferable to utilize between about 150 grams and about190 grams of pressurized medium 36 with the oxygen being between about10% to about 30% of this medium 26 on a molar basis. More specifically,when about 169 grams of the pressurized medium 36 is utilized, withabout 15% of this on a mole percentage basis being oxygen, the totalweight of the propellant grains 90 may be about 10.4 grams.

The above-identified reduction in the amount of propellant in accordancewith the present invention in comparison to the above-identified FN1061-10 propellant composition may be expressed as a ratio of the weightof the pressurized medium 36 to the total weight of propellant grains90. With regard to the FN 1061-10 propellant, the assignee of thisapplication presently uses a ratio of about 7.04 for the weight of argon(i.e., the stored gas and corresponding with the pressurized medium 36associated with the present invention) to the weight of FN 1061-10propellant. With regard to the present invention, the ratio of theweight of the pressurized medium 36 to the total weight of thepropellant grains 90 ranges from about 10 to about 20, and morepreferably from about 14 to about 18, and is most preferably greaterthan about 15. As can be appreciated, these ratios may be furtherincreased by use of hotter propellants, which would require even lesspropellant. In this regard, because the output gases of propellants inaccordance with principles of the present invention are essentially freeof hot particulate matter, the inflator can produce output gases at ahigher temperature than can a particulate-laden inflator such as currentstate-of-the-art hybrids. This increase in temperature will allow theinflator to be smaller and lighter still, since the hotter gas isrelatively more expansive.

The above-identified reduction in the amount of propellants inaccordance with the present invention in comparison to theabove-identified FN 1061-10 propellant composition may also be expressedas a ratio of the gram moles of the total gas output (i.e., thecombination of the propellant gases and the pressurized medium 36) tothe total weight of the propellant grains 90. With regard to the FN1061-10 propellant, the assignee of the application presently uses aratio of about 0.192 gram moles/gram of propellant for the moles of theoutput gas to the weight of the propellant. In comparison and withregard to the present invention, the ratio of the moles of the outputgas to the total weight of the propellant grains 90 ranges from about0.35 gram moles per gram of propellant to about 0.6 gram moles per gramof propellant, more preferably from about 0.4 gram moles per gram ofpropellant to about 0.5 gram moles per gram of propellant and is mostpreferably about 0.5 gram moles per gram of propellant.

Weight reductions are of course realized by merely reducing the totalweight of the propellant grains 90. However, this reduction in theamount of propellant also allows for a size reduction for the gasgenerator 82, and thus the weight of the gas generator 82. Consequently,the size of the inflator housing 34 can be similarly reduced. Therefore,the size of the entire inflator 30 may be reduced. Although varioussizes of inflators may be used depending upon the application and/ordesign considerations, in comparison to using the above-identified FN1061-10 propellant in a given inflator design, the propellants of thepresent invention allow for a size reduction typically of about 50%percent (and also a 50% weight reduction).

The use of multiple gases for the pressurized medium 36 allows for theuse of a gun type propellant for the propellant grain 90. Generally, thepressurized medium 36 is composed of one inert gas and oxygen.Appropriate inert gases include argon, nitrogen, helium, and neon, withargon being preferred. The oxygen portion of the pressurized medium ismulti-functional. Initially, the reaction of the oxygen with thecombustion byproducts of the gun type propellant of the propellant grainprovides a source of heat which contributes to the expansion of theinert gas. This allows at least in part for a reduction in the amount ofpropellant which is required for the gas generator 82. Moreover, thereaction of the oxygen with the combustion byproducts also reduces anyexisting toxicity levels of the propellant gases. For instance, theoxygen will convert existing carbon monoxide to carbon dioxide, existinghydrogen to water vapor, and unburned hydrocarbons will be similarlyeliminated.

As noted, the amount of the one inert gas, on a molar basis, is betweenabout 70% and about 90% and the amount of oxygen, on a molar basis, isbetween about 10% and about 30%. Generally, it is desirable to use anamount of oxygen in excess of that based upon theoretical conversions.However, it is also generally desirable to not have more than about 20%(molar) oxygen in the output gas (i.e., the combination of thepropellant gases and the pressurized medium).

The inflator 30 may be assembled in the following manner. Initially, thegas generator 82 is assembled, such as by: 1) inserting the baffle 100and screen 104 in the gas generator housing 86 adjacent the dischargeend 96; 2) inserting the propellant sleeve 94 in the gas generatorhousing 86; 3) positioning the propellant grains 90 within thepropellant sleeve 94; 4) inserting the baffle 100 and screen 104 in thegas generator housing 86 adjacent the end of the propellant sleeve 94;5) inserting the primer holder 116, with the ignition/booster material144 and charge cup 148, in the gas generator housing 86; and 6)inserting the actuation guide 140, belleville washer 136, and actuationpiston 124 into the gas generator housing 86. Thereafter, the variousparts are interconnected, such as by welding the gas generator housing86 to the orifice sleeve 74, by welding the diffuser 38 to the boss 66after positioning the projectile 50 and initiator 46 in the diffuser 38,welding the closure disk 70 between the boss 66 and orifice sleeve 74,and welding the boss 66 to the inflator housing 34. With the abovestructure in tact, the pressurized medium 36 may be introduced into theinflator housing 34. In this regard and in the case of multiple gases,the argon and oxygen may be separately introduced into the inflatorhousing 34 through the end plug 42 which is welded to the end of theinflator housing 34.

The following examples further assist in the description of variousfeatures associated with the present invention.

EXAMPLE 1

The above-noted HPC-96 propellant was used to form the propellant grains90 having a total weight of 18 grams. Each propellant grain 90 had theconfiguration generally illustrated in FIG. 2, and had a length orthickness of about 0.52 inches, an outer diameter of about 0.29 inches,and a web thickness of about 0.105 inches (one-half of the differencebetween the inner and outer diameters of the propellant grain 90).Moreover, the HPC-96 propellant had the following properties whenignited in the presence of air: an impetus of 363,493 ft-lbs/lb; a heatof explosion of 1,062 calories/gram; a T_(v) of 3490° K.; a molecularweight of the gases of 26.7 moles; a specific heat ratio of 1.2196; anda solid density of 1.65 grams/cubic centimeter. The gas composition,based upon theoretical calculations of normal compositions and assuminga combustion at 25,000 psig expanded to atmospheric pressure, on a molarpercentage basis, was: about 26.5% carbon monoxide; about 19.1% water;about 26.2% carbon dioxide; about 13.7% nitrogen; about 14.2% hydrogen;and about 0.3% other gases.

When the propellant grains 90 of HPC-96 were subjected to a temperatureof 120° C., the grains 90 began to discolor within about 40 minutes andignited within about 5 hours. This reduces the desirability of using theHPC-96 propellant for the propellant grains 90 since one currentindustry standard requires that a propellant for an inflatable safetysystem does not degrade substantially when exposed to a temperature of107° C. for a period of 400 hours, and that the propellant thereafterignite when exposed to its autoignition temperature. However, the HPC-96propellant does illustrate certain principles of the present inventionand is thus included herein.

With regard to HPC-96 propellant grains 90, about 169 grams of thepressurized medium 36 was provided to the inflator housing 34 andconsisted, on a molar percentage basis, of about 5% oxygen and about 95%argon. The inflator 30 had four orifice ports 78 on the orifice sleeve74 with each having a diameter of about 0.266", and the gas generatornozzle 98 had a diameter of about 0.469". The pressure variation withinthe inflator housing 34 during operation of the inflator 30 was similarto that presented in FIG. 3, and the pressure within a 100 liter tankfluidly interconnected with the inflator 30 was similar to thatillustrated in FIG. 4 and is generally representative of the pressurebuildup within the air/safety bag 18. The gaseous output from theinflator 30 included, on a weight percentage basis, about 1.2% carbonmonoxide, about 1.5% carbon dioxide, greater than about 2% hydrogen, andabout 60 ppm of NO_(x). Consequently, the use of argon and oxygen in thenoted proportions significantly reduced the amount of carbon monoxideand hydrogen when compared theoretical gaseous output of the HPC-96propellant noted above.

EXAMPLE 2

The procedure of Example 1 was repeated but 10.4 grams of HPC-96propellant was used for the grains 90 and about 164.4 grams of apressurized medium 36 was used with the composition being a molarpercentage basis, about 15% oxygen and about 85% argon. The performancecurves for the inflator 30 when actuated with these propellant grains 90are illustrated in FIGS. 3 and 4. Moreover, the gaseous output from theinflator 30 included, on a molar percentage basis, about 2.4% carbondioxide, about 1000 ppm carbon monoxide, about 70 ppm NO_(x), about 38ppm NO₂, and about 0 ppm of hydrogen. Consequently, with the increase inthe amount of oxygen to 15% from the 5% of Example 1, the amount ofcarbon monoxide was significantly reduced without an appreciable effectupon NO₂. Moreover, this also allowed for the use of significantly lesspropellant.

EXAMPLE 3

The procedure of Example 1 was repeated twice using 10.4 grams of HPC 96and 169.0 grams of pressurized medium 36 composed, on a molar percentagebasis, of about 15% oxygen and about 85% argon. The performance curvesfor the inflator 30 were similar to those presented in FIGS. 3-4.Moreover, the gaseous output from the inflator 30 included about 1000ppm and 800 ppm carbon monoxide, respectively, about 1.0% and 1.2%carbon dioxide, respectively, about 60 ppm and 50 ppm NO_(x),respectively, and about 23 ppm and 20 ppm NO₂, respectively.Consequently, the increase in the amount of oxygen to 15% and thereduction of the amount of HPC 96 reduced the amount of carbon monoxidewithout an appreciable effect upon NO₂. Moreover, the increased amountof oxygen allowed for the use of less propellant.

The foregoing description of the invention has been presented forpurposes of illustration and description. Furthermore, the descriptionis not intended to limit the invention to the form disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, and the skill or knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain best modes known ofpracticing the invention and to enable others skilled in the art toutilize the invention in such, or other, embodiments and with thevarious modifications required by the particular applications or uses ofthe invention. It is intended that the appended the claims be construedto include alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. A method for assembling an inflator for aninflatable safety system comprising an air/safety bag, said inflatorcomprising an inflator housing, a gas generator, and an inflatoractivation assembly, said method comprising the steps of:positioning asolid gun type propellant inside said gas generator, wherein combustionof said solid gun type propellant augments a flow to the air/safety bagand wherein exposure of said gun type propellant to a temperature of 107degrees for a period of 400 hours does not degrade said gun typepropellant substantially in relation to its suitability for use in saidinflator, and thereafter said gun type propellant will ignite whenexposed to an autoignition temperature of said gun type propellant;positioning said gas generator inside said inflator housing;interconnecting said gas generator and said inflator housing;interconnecting said inflator activation assembly with said inflatorhousing, said activation assembly comprising an ignitable material otherthan said gun type propellant; introducing a first gas into at leastsaid inflator housing; introducing a second gas into at least saidinflator housing which is different from said first gas, wherein saidfirst and second gases consist essentially of an inert gas and oxygen,respectively; and sealing said inflator housing to substantially retainsaid first and second gases within said inflator housing, wherein aftersaid sealing step and prior to any activation of said inflatoractivation assembly, said first and second gases are the only gasescontained within said inflator housing and define a pressurized medium.2. A method, as claimed in claim 1, wherein:said positioning a gun typepropellant step comprises positioning from about 10 grams to about 12grams of said gun type propellant within said gas generator.
 3. Amethod, as claimed in claim 1, wherein:said positioning a gun propellantstep comprises positioning less that about 15 grams of said gun typepropellant within said gas generator.
 4. A method, as claimed in claim2, wherein:said method further comprises the step of pressurizing saidinflator housing with an amount of said first and second gases rangingfrom about 150 grams to about 190 grams using said introducing a firstgas and introducing a second gas steps.
 5. A method, as claimed in claim1, wherein:said method further comprises the step of selecting an amountof said pressurized medium for said introducing first and second gasessteps and selecting an amount of said gun type propellant for saidpositioning step, whereby a ratio of a weight of said pressurized mediumto a weight of said gun type propellant is within at least one of firstand second ranges, said first range being from about 14 to about 18 andsaid second range being greater than about
 15. 6. A method, as claimedin claim 5, wherein:said selecting step comprises selecting a gun typepropellant having a composition, on a weight percentage basis, of about76.0% hexahydrotrinitrotriazine, about 12.0% percent cellulose acetatebutyrate, about 4.0% nitrocellulose of which about 12.6% is nitrogen,about 7.60% acetyl triethyl citrate, and about 0.4% ethyl centralite. 7.A method, as claimed in claim 1, wherein:said first gas is argon andsaid second gas is oxygen, said first and second gases are a pressurizedmedium, said introducing a first gas step comprises, on a molar basis,introducing about 70% to about 90% of said pressurized medium with saidargon, and said introducing a second gas step comprises, on a molarbasis, introducing about 10% to about 30% of said pressurized mediumwith said oxygen.